Oracle 12C RAC的optimizer_adaptive_features造成数据插入超时
问题分析
使用10046事件追踪方式，直接生成上传时的数据库事件日志进行分析，发现主要区别在于以下两条sql语句在每次长时间上传时都有出现，并且执行用户不是上传用户，而是数据库SYS用户。
********************************************************************************
SQL ID: frjd8zfy2jfdq Plan Hash: 510421217
SELECT executions, end_of_fetch_count, elapsed_time/px_servers
elapsed_time, cpu_time/px_servers cpu_time,
buffer_gets/executions buffer_gets
FROM
(SELECT sum(executions) as executions, sum(case
when px_servers_executions > 0 then
px_servers_executions else executions end)
as px_servers, sum(end_of_fetch_count) as end_of_fetch_count,
sum(elapsed_time) as elapsed_time,
sum(cpu_time) as cpu_time, sum(buffer_gets) as
buffer_gets FROM gv$sql
WHERE executions > 0 AND sql_id = :1
AND parsing_schema_name = :2)
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 64 0.00 0.00 0 0 0 0
Execute 64 0.24 0.91 0 0 0 0
Fetch 64 0.14 0.42 0 0 0 64
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 64 0.00 0.00 0 0 0 0
Execute 64 0.24 0.91 0 0 0 0
Fetch 64 0.14 0.42 0 0 0 64
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 192 0.39 1.34 0 0 0 64
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS (recursive depth: 1)
Number of plan statistics captured: 64
Rows (1st) Rows (avg) Rows (max) Row Source Operation
---------- ---------- ---------- ---------------------------------------------------
1 1 1 VIEW (cr=0 pr=0 pw=0 time=20602 us)
1 1 1 SORT AGGREGATE (cr=0 pr=0 pw=0 time=20596 us)
0 0 0 PX COORDINATOR (cr=0 pr=0 pw=0 time=20573 us)
0 0 0 PX SEND QC (RANDOM) :TQ10000 (cr=0 pr=0 pw=0 time=0 us)
0 0 0 VIEW GV$SQL (cr=0 pr=0 pw=0 time=0 us)
0 0 0 FIXED TABLE FIXED INDEX X$KGLCURSOR_CHILD (ind:2) (cr=0 pr=0 pw=0 time=0 us)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ PX Deq: reap credit 1448 0.00 0.02
PX Deq: Join ACK 193 0.00 0.25
IPC send completion sync 128 0.00 0.08
PX Deq: Parse Reply 128 0.06 0.24
PX Deq: Execute Reply 128 0.00 0.06
reliable message 64 0.00 0.06
PX Deq: Signal ACK EXT 128 0.00 0.01
PX Deq: Slave Session Stats 128 0.00 0.01
enq: PS - contention 66 0.00 0.09
KJC: Wait for msg sends to complete 5 0.00 0.00
latch: shared pool 1 0.00 0.00
********************************************************************************
SQL ID: 4b4wp0a8dvkf0 Plan Hash: 4033942373
SELECT executions, end_of_fetch_count, elapsed_time/px_servers
elapsed_time, cpu_time/px_servers cpu_time,
buffer_gets/executions buffer_gets
FROM
(SELECT sum(executions_delta) as EXECUTIONS,
sum(case when px_servers_execs_delta > 0
then px_servers_execs_delta else
executions_delta end) as px_servers,
sum(end_of_fetch_count_delta) as end_of_fetch_count,
sum(elapsed_time_delta) as ELAPSED_TIME, sum(cpu_time_delta)
as CPU_TIME, sum(buffer_gets_delta) as BUFFER_GETS
FROM DBA_HIST_SQLSTAT s,
V$DATABASE d, DBA_HIST_SNAPSHOT sn
WHERE s.dbid = d.dbid
AND bitand(nvl(s.flag, 0), 1) = 0 AND
sn.end_interval_time > (select
systimestamp at TIME ZONE dbtimezone from dual) - 7
AND s.sql_id = :1
AND s.snap_id = sn.snap_id AND
s.instance_number = sn.instance_number AND s.dbid = sn.dbid
AND parsing_schema_name = :2)
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 64 0.00 0.00 0 0 0 0
Execute 64 0.08 0.08 0 0 0 0
Fetch 64 0.13 0.27 0 1170 0 64
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 192 0.21 0.36 0 1170 0 64
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS (recursive depth: 1)
Number of plan statistics captured: 3
Rows (1st) Rows (avg) Rows (max) Row Source Operation
---------- ---------- ---------- ---------------------------------------------------
1 1 1 VIEW (cr=18 pr=0 pw=0 time=6289 us cost=17 size=78 card=1)
1 1 1 SORT AGGREGATE (cr=18 pr=0 pw=0 time=6282 us)
0 0 0 NESTED LOOPS (cr=18 pr=0 pw=0 time=6263 us cost=15 size=124 card=1)
0 0 0 NESTED LOOPS (cr=18 pr=0 pw=0 time=6258 us cost=15 size=124 card=1)
0 0 0 HASH JOIN (cr=18 pr=0 pw=0 time=6256 us cost=14 size=97 card=1)
0 0 0 NESTED LOOPS (cr=18 pr=0 pw=0 time=6244 us cost=14 size=97 card=1)
0 0 0 STATISTICS COLLECTOR (cr=18 pr=0 pw=0 time=6241 us)
0 0 0 NESTED LOOPS (cr=18 pr=0 pw=0 time=6223 us cost=13 size=81 card=1)
1 1 1 MERGE JOIN CARTESIAN (cr=0 pr=0 pw=0 time=5648 us cost=0 size=10 card=1)
1 1 1 FIXED TABLE FULL X$KCCDI (cr=0 pr=0 pw=0 time=3449 us cost=0 size=10 card=1)
1 1 1 BUFFER SORT (cr=0 pr=0 pw=0 time=2187 us cost=0 size=0 card=1)
1 1 1 FIXED TABLE FULL X$KCCDI2 (cr=0 pr=0 pw=0 time=2136 us cost=0 size=0 card=1)
0 0 0 PARTITION RANGE ITERATOR PARTITION: KEY KEY (cr=18 pr=0 pw=0 time=568 us cost=13 size=71 card=1)
0 0 0 TABLE ACCESS BY LOCAL INDEX ROWID BATCHED WRH$_SQLSTAT PARTITION: KEY KEY (cr=18 pr=0 pw=0 time=511 us cost=13 size=71 card=1)
0 0 0 INDEX RANGE SCAN WRH$_SQLSTAT_INDEX PARTITION: KEY KEY (cr=18 pr=0 pw=0 time=477 us cost=11 size=0 card=2)(object id 8299)
0 0 0 TABLE ACCESS BY INDEX ROWID WRM$_SNAPSHOT (cr=0 pr=0 pw=0 time=0 us cost=1 size=16 card=1)
0 0 0 INDEX UNIQUE SCAN WRM$_SNAPSHOT_PK (cr=0 pr=0 pw=0 time=0 us cost=0 size=0 card=1)(object id 8695)
0 0 0 TABLE ACCESS FULL WRM$_SNAPSHOT (cr=0 pr=0 pw=0 time=0 us cost=1 size=16 card=1)
0 0 0 INDEX UNIQUE SCAN WRM$_SNAPSHOT_PK (cr=0 pr=0 pw=0 time=0 us cost=0 size=0 card=1)(object id 8695)
0 0 0 TABLE ACCESS BY INDEX ROWID WRM$_SNAPSHOT (cr=0 pr=0 pw=0 time=0 us cost=1 size=27 card=1)
0 0 0 FAST DUAL (cr=0 pr=0 pw=0 time=0 us cost=2 size=0 card=1)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
Disk file operations I/O 3 0.00 0.00
control file sequential read 448 0.00 0.18
********************************************************************************
经过资料分析，这两条语句是由于开通了Oracle 12C的新功能而产生的，此功能为“optimizer_adaptive_features”。其主要功能是为了在语句执行过程中实时收集表的统计信息，方便Oracle选择更准确的执行计划。
但是，这个功能在RAC非常损耗性能，因为它需要查找全局视图gv$sql的数据，在多个实例的情况下会进行并发执行，参考这篇资料。
因为“optimizer_adaptive_features”参数宣称在OLAP数据仓库环境中可以获得较好的效果，实际在重上传轻查询的OLTP系统上，可以关闭这项新功能。
实验测试
因为该参数支持会话级别和系统级别调整，因为可以在单独一个会话内测试下插入时间和查询时间。
- 插入测试
采用同时提交多条TARGETTABLE数据。
打开“optimizer_adaptive_features”时为2.2秒，关闭该功能时为0.375。
- 查询测试
采用系统中执行最多的语句进行测试。
打开“optimizer_adaptive_features”时为0.05秒，关闭该功能时为0.02秒。
- 关闭方式
因为“optimizer_adaptive_features”为动态参数，在系统级别修改时不需要重启。已在测试环境试验可用。
执行语句为
alter system set optimizer_adaptive_features=false scope=both;
版权说明:camash原创，转载请注明出处 http://www.cnblogs.com/shenfeng/
--EOF--
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